1. Field of the Invention
The present invention relates to a wiring board capable of forming a wiring circuit to which electronic parts are joined without using solder joint.
2. Description of Related Art
Wiring boards are formed as laminated boards where an insulating board and a conductive layer made of copper foil or the like are laminated and a wiring pattern is formed in the conductive layer by etching or the like. In addition, electronic parts such as ICs (Integrated Circuits) and LSIs (Large Scale Integrated circuits) are joined, by means of soldering, and mounted onto the conductive layer where the wiring pattern has been formed, and thereby, a wiring circuit is formed. Here, such electronic parts have a configuration such that a semiconductor chip made by cutting a wafer into pieces is joined to and mounted on the surface of an insulating board, a surface on which wiring has been formed, of a circuit board where a metal conductive board and the insulating board are laminated.
In addition, Japanese Patent Application Laid-Open No. 2001-223471, for example, discloses a method for manufacturing a wiring board in the following. First, a first printed circuit board where plural first conductive wires are placed parallel to each other on one surface of a first resin sheet and a second printed circuit board where plural second conductive wires are placed parallel to each other on one surface of a second resin sheet are laminated in such a manner that the first conductive wires and the second conductive wires cross at right angles. Then, electrical connections are made by irradiating the intersections of the first conductive wires and the second conductive wires with a laser beam under a state where an insulating layer is inserted between the first conductive wires and the second conductive wires. As a result of the above, a wiring circuit is formed on a wiring board.
Wiring boards inevitably resonate when they are utilized in an environment in which relatively large vibration occurs such as in the case where a wiring board is placed in the proximity to an electric motor, an internal combustion engine or the like or in the case where it is mounted in a vehicle. Therefore, when a conventional wiring board, wiring circuit of which has been formed by joining electronic parts to the wiring board by soldering is utilized in such an environment, the solder joints of the electronic parts become fragile due to resonance as described above, and therefore, a problem arises such that a solder joint is easily broken. In addition, electronic parts are joined to a conventional wiring board by soldering so that a wiring circuit is formed, and therefore, miniaturization is restricted and an improvement measure in related to this has been demanded. Furthermore, a relatively strong joining force has been obtained by utilizing a solder including lead in a conventional solder joint. However, lead is not an environmentally friendly substance, and therefore, utilization of a solder not including lead has been required from the point of view of reduction of a substance that is not environmentally friendly. In the case where such a so-called Pb free solder is utilized for conventional wiring board, currently solder joints tend to become fragile.
In addition, according to the invention disclosed in the above described Japanese Patent Application Laid-Open No. 2001-223471, the first and second printed circuit boards where plural conductive wires are placed parallel to each other on each of the two resin sheets are required, and therefore, the structure inevitably become complicated. In addition, electrical connections at the intersections of the first conductive wires and the second conductive wires are made by welding using a laser beam or the like, and therefore, a problem arises such that a joint between a first conductive wire and a second conductive wire is easily broken in response to resonance in the case where the wiring board is mounted in a vehicle or the like. Furthermore, a problem arises such that a defect easily occurs in a contact due to a thermal impact, wearing caused by plasma and the like in addition to a problem in response to resonance as described above.